Vertical capacitor contact arrangement and fabrication method

ABSTRACT

An arrangement for making electrical contact to a vertical capacitor having top and bottom metal layers separated by a dielectric, and at least one trench. Recesses are formed in an oxide layer over the capacitor to provide access to the top and bottom metal layers. The recesses include contacting portions preferably positioned such that there is no overlap between them and any of the trenches. Metal in the recesses, preferably copper, forms electrical contacts to the vertical capacitor&#39;s metal layers and enables reliable bonding to copper metallization on other layers such as an ROIC layer. ‘Dummy’ capacitors may be tiled on portions of the IC where there are no vertical capacitors, preferably with the top surfaces of their top metal at a height approximately equal to that of the top surface of the vertical capacitor&#39;s top metal, thereby enabling the IC to be planarized with a uniform planarization thickness.

GOVERNMENT LICENSE RIGHTS

This invention was made with Government support under contractW31P4Q-09-C-0513 awarded by the Defense Advanced Research ProjectsAgency (DARPA). The Government has certain rights in this invention.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates generally to vertical capacitors on integratedcircuits (ICs), and more particularly to a vertical capacitor contactarrangement and method of fabricating same.

Description of the Related Art

A conventional imaging array comprises an array of pixels, each of whichincludes a photodetector and the input circuit of a “readout IC” (ROIC)which contains both a capacitor which stores the charge generated by thephotodetector in response to light, and electrical circuitry to conveythe charge from the photodiode to the capacitor and from the capacitorto further processing circuitry of the ROIC. The ROIC and charge storagecapacitors are typically fabricated together using an electronic circuitprocess, such as CMOS, with the size of each charge storage capacitorlimited in part by the size of each pixel and the complexity of thecircuit.

Problems may arise when a high-density imaging array is needed. A higherdensity array requires that the pixel size be small. However, asignificant limitation is encountered when attempting to scale tosmaller pixel size, in that a smaller pixel necessitates a smallercharge storage capacitor, which serves to reduce the amount of chargethat can be stored. This has an adverse effect on the array'ssensitivity, typically reflected in the “noise equivalent differentialtemperature” (NEDT) value, which is a measure of the lowest signal fluxlevel that can be detected by the array. The NEDT value might be loweredby making the charge storage capacitors larger, but this would consumecircuit area that might otherwise be used to increase circuitfunctionality. These factors combine to impede the realization of highperformance (low NEDT), high-functionality imaging arrays with smallpixel pitch.

One way of overcoming the limitations associated with the ROIC andcharge storage capacitors being fabricated together is to provide aseparate charge storage capacitor layer which is distinct from thephotodetector and ROIC layers; the layers are electricallyinterconnected to form the array. The capacitors within the chargestorage capacitor layer may be, for example, vertical capacitorscomprising a microstructured surface coated with sequentialconductive-insulating-conductive thin-film coatings. However, problemscan arise with some vertical capacitor designs. Electrical contact needsto be made to the top and bottom conductive layers of each capacitor. Insome cases, the recesses in which metal is deposited to make contact tothe top conductive layer can be overetched. The corners of the tops ofthe walls between the trenches are particularly vulnerable tooveretching. This can result in damage to or breaching of the dielectriclayer which results in reduced breakdown voltage or shorting. Inaddition, the trenches are often not completely filled with theplanarizing oxide layer, but merely pinched off. Overetching can breachthe pinchoff area, opening the voids in the trenches to copper platingwhich results in plating non-uniformity and extra stress duringsubsequent thermal cycling events.

The overetching problem is exacerbated at the edges of a capacitor arraywhere there is a sharp step from the plateau of the array down to therest of the field. The chemical-mechanical planarization process acts tosmooth out this transition, resulting in an extra thin layer ofplanarization oxide at the edges of the field.

SUMMARY OF THE INVENTION

A contact arrangement for making electrical contact to a verticalcapacitor on an integrated circuit (IC) is presented, which addressesseveral of the problems noted above.

The contact arrangement is for use with a vertical capacitor having atop metal and a bottom metal separated by a dielectric, and at least onetrench. The arrangement requires a first oxide layer over the verticalcapacitor, and a recess in the first oxide layer which provides accessto one of the vertical capacitor's top or bottom metal layers. Metaldeposited in the recess forms an electrical contact to the verticalcapacitor's metal layer. The metal is preferably copper, which enablesreliable bonding to copper metallization on other layers such as an ROIClayer.

Each recess includes a contacting portion which contacts the top metal.The vertical capacitor typically comprises at least two adjacenttrenches, with the contacting portion of a recess approximately centeredbetween adjacent trenches such that there is no overlap between thecontacting portion and any of said trenches. A recess providing accessto the vertical capacitor's top metal is preferably T-shaped, with thevertical portion of the T being the contacting portion. In this way, theoveretching issues described above may be avoided. The present contactarrangement is typically employed to provide contact to an array ofvertical capacitors, each of which has a top metal and a bottom metalseparated by a dielectric and at least one trench.

‘Dummy’ capacitors may be tiled on portions of the IC where there are novertical capacitors, arranged such that the top surfaces of their topmetal are at a height approximately equal to that of the top surface ofthe vertical capacitor's top metal. This enables the IC to be planarizedwith a uniform planarization thickness.

These and other features, aspects, and advantages of the presentinvention will become better understood with reference to the followingdrawings, description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an IC which includes the present verticalcapacitor contact arrangement.

FIG. 2 is a diagram illustrating an IC which includes the presentvertical capacitor contact arrangement as it might be used withadditional ICs or device layers.

FIG. 3 is a sectional view of an IC which includes the present verticalcapacitor contact arrangement and has been planarized.

FIG. 4 is a sectional view of an IC which includes the present verticalcapacitor contact arrangement and a dummy capacitor, over which a secondlayer of oxide has been deposited.

FIG. 5 is a sectional view of the IC of FIG. 4, after it has beenplanarized.

FIG. 6 is a sectional view of an IC which includes the present verticalcapacitor contact arrangement on an IC which includes a dummy capacitor.

FIG. 7a-7m are sectional views illustrating one possible fabricationsequence for providing the present vertical capacitor contactarrangement on an IC.

DETAILED DESCRIPTION OF THE INVENTION

The present contact arrangement is for making electrical contact to avertical capacitor on an IC, in which the capacitor includes a top metaland a bottom metal separated by a dielectric, and at least one trench.The contact arrangement is illustrated in the sectional view of a firstIC 10, shown in FIG. 1. The vertical capacitor includes a top metallayer 12 and a bottom metal layer 14 separated by a dielectric 16,formed into a structure which includes at least one trench; two trenches18, 20 are shown in the exemplary embodiment of FIG. 1 though a typicalvertical capacitor (per pixel)has about 5 trenches. The top and bottommetal layers preferably comprise TiN. The dielectric layer 16 betweenthe top and bottom metals preferably comprises hafnium oxide.

The contact arrangement is effected by providing a dielectric layer 22,preferably silicon dioxide, over the vertical capacitor. A recess isformed in dielectric layer 22 which provides access to one of thevertical capacitor's top or bottom metal layers; FIG. 1 includes a firstrecess 24 which provides access to top metal layer 12 and a secondrecess 26 which provides access to bottom metal layer 14.

Metal is formed in each recess to provide electrical contact to themetal layer the recess provides access to. Thus, in FIG. 1, metal 28 isformed in first recess 24 and provides electrical contact to top metallayer 12, and metal 30 is formed in second recess 26 and provideselectrical contact to bottom metal layer 14.

As shown in FIG. 1, a recess 24 which provides access to the verticalcapacitor's top metal 12 includes a contacting portion 31 which contactsthe top metal; the contacting portion is preferably narrower than theupper portion of the recess. A vertical capacitor typically comprises atleast two adjacent trenches, such as trenches 18 and 20 in FIG. 1; whenso arranged, the contacting portion 31 of a recess is approximatelycentered between adjacent trenches such that there is no overlap betweenthe contacting portion and any of the trenches. This reduces the chancesof overetching at the trench corners. Though recess 24 can have a numberof different shapes, it is preferably T-shaped as shown in FIG. 1, withthe narrower vertical portion of the T being the contacting portion. Thehorizontal top portion of the T-shaped recess should have a top surfacearea that is sufficient for subsequent bonding processes.

Positioning the recesses such that there is no overlap between acontacting portion of a recess and any of the trenches reduces thechances of overetching at the vulnerable trench corners, therebyavoiding shorting problems that might otherwise arise. This recesspositioning also serves to avoid overetching that might otherwise resultin breaching oxide pinch-off in the vertical capacitor trenches 18, 20,as the dielectric 22 over the trenches is left unetched.

The metal 28, 30 formed in the recesses is preferably copper. The copperserves to provide electrical contact to the capacitor's metal layers, aswell as serving as an effective bonding contact with which to provideinterconnection to other structures. For example, a second IC orsemiconductor layer may need to be interconnected to one or morevertical capacitors on first IC 10 via one or more electrical contacts.One way to effect this is to provide electrical contacts on the secondIC and on IC 10 that make contact to each other when the ICs are alignedin a predetermined manner This is illustrated in FIG. 2. Here, first IC10 includes vertical capacitors represented by capacitor 40, whichincludes a contact 42, preferably copper, formed as described herein. Asecond IC 44 with which IC 10 is to be interconnected includes a contact46, also preferably copper. To effect the interconnection between ICs 10and 44, contacts 42 and 46 are pressed together such that a bond isformed.

Second IC 44 might be, for example, a readout IC (ROIC). Such a systemmight also include a third IC or layer 50 which includes an array ofphotodetectors 52. Here, IC 10 would typically include an array ofvertical capacitors 40 which serve as charge storage capacitors for thephotodetector array. ROIC 44 would typically comprise a meteringcircuit—preferably a direct injection transistor 54—between eachphotodetector and charge storage capacitor, and a switch 56 between eachcharge storage capacitor and a pixel column busline 58; each pixel ofthe array would typically include one of each of these components.

A problem can arise under certain circumstances when employing avertical capacitor structure with the present contact arrangement; thisis illustrated in FIG. 3. Due to the structure of the verticalcapacitors, materials such as an oxide layer 60 deposited over the ICcan result in as much as 5500A more material over the capacitors 62 ascompared with the areas 64 without capacitors. If the IC is thenplanarized (chemical-mechanical planarization (CMP), for example), theplanarization thins the oxide more at the edge of the array than in thecenter, which is undesirable as the thin oxide may result in overetchingand shorting.

One possible solution to this problem is shown in FIG. 4. An ICsubstrate 70 includes at least one vertical capacitor 72, but furthercomprises one or more dummy capacitors 74 tiled on portions of the ICwhere there are no vertical capacitors. The dummy capacitors arepreferably arranged such that the top surfaces of their top metal layer76 are at a height approximately equal to that of the top surface 78 ofthe vertical capacitor's top metal layer. With dummy capacitors tiled asdescribed, planarizing an oxide layer 80 deposited over the oxide layer82 immediately above the vertical capacitor structures results in anoxide layer of uniform thickness. This is illustrated in FIG. 5.Eliminating thickness variation across the array in this way can avoidoveretching and shorting that might otherwise occur.

The use of the present contact arrangement with an IC containing bothvertical capacitors and dummy capacitors as described herein is shown inFIG. 6. Additional recesses are formed and filled with metal to providecontacts 84 to the dummy capacitors if needed.

One possible process for fabricating vertical capacitors and a contactarrangement as described herein is illustrated in FIGS. 7a-7m . In FIG.7a , a substrate 100, preferably silicon, is provided, and an oxide hardmask 102, preferably TEOS oxide, is deposited on the substrate. Trenches104 are next patterned and etched in substrate 100: in FIG. 7b , theoxide is etched where trenches are to be formed, and in FIG. 7c , thesilicon substrate is etched to complete the trenches.

The capacitor layers are deposited next. In FIG. 7d , a bottom metallayer 106 is deposited, suitably TiN and 500 Å thick, followed by adielectric layer such as an oxide layer 108, suitably hafnium oxide and500 Å thick, and a top metal layer 110 (suitably TiN/500 Å). This isfollowed by an oxide deposition 112 over the entire IC.

In FIG. 7e , oxide layer 108 and top metal layer 110 are etched asneeded to begin the process of providing access to bottom metal layer106. Access is completed in FIG. 7f with the etching of oxide layer 108down to bottom metal layer 106.

Another oxide layer 114, suitably TEOS oxide 10,000 Å thick, isdeposited over the IC in FIG. 7g , which is then planarized in FIG. 7h .In FIGS. 7i and 7j , oxide layers 114 and 112 are etched to formrecesses 116 for accessing the top metal layers of the verticalcapacitors and recesses 118 for accessing the bottom metal layers.Recesses providing access to the top metal layer of a vertical capacitorare preferably T-shaped.

Contact metal 120 is deposited over the entire IC in FIG. 7k . Metal 120is preferably copper (suitably 7000 Å thick), with the copper depositionpreferably preceded by the deposition of a seed layer 122, preferablytantalum and copper. Following an anneal, a planarization step isperformed as shown in FIG. 7l . Finally, in FIG. 7m , oxide layer 114 isetched to expose the top portions of the electrical contacts.

The process depicted in FIGS. 7a-7m is merely exemplary; there arenumerous means by which a vertical capacitor contact arrangement asdescribed herein could be fabricated.

The embodiments of the invention described herein are exemplary andnumerous modifications, variations and rearrangements can be readilyenvisioned to achieve substantially equivalent results, all of which areintended to be embraced within the spirit and scope of the invention asdefined in the appended claims.

1. A vertical capacitor contact arrangement for making electricalcontact to a vertical capacitor on a first integrated circuit (IC), saidvertical capacitor having a top metal and a bottom metal separated by adielectric, and at least one trench, comprising: a first oxide layerover said vertical capacitor and in said at least one trench; a recessin said first oxide layer which provides access to one of said verticalcapacitor's top or bottom metal layers; and metal in said recess suchthat said metal provides an electrical contact to the top or bottommetal layer to which said recess provides access.
 2. A verticalcapacitor contact arrangement for making electrical contact to avertical capacitor on a first integrated circuit (IC), said verticalcapacitor having a top metal and a bottom metal separated by adielectric, and at least one trench, comprising: a first oxide layerover said vertical capacitor; a recess in said first oxide layer whichprovides access to one of said vertical capacitor's top or bottom metallayers; and metal in said recess such that said metal provides anelectrical contact to the top or bottom metal layer to which said recessprovides access; wherein said metal is copper.
 3. The contactarrangement of claim 1, wherein said recess provides access to saidvertical capacitor's top metal, said recess having a contacting portionwhich contacts said top metal.
 4. The contact arrangement of claim 3,wherein said vertical capacitor comprises at least two adjacenttrenches, said contacting portion of said recess approximately centeredbetween adjacent ones of said trenches such that there is no overlapbetween said contacting portion and any of said trenches.
 5. A verticalcapacitor contact arrangement for making electrical contact to avertical capacitor on a first integrated circuit (IC), said verticalcapacitor having a top metal and a bottom metal separated by adielectric, and at least one trench, comprising: a first oxide layerover said vertical capacitor; a recess in said first oxide layer whichprovides access to said vertical capacitor's top metal layer, saidrecess having a contacting portion which contacts said top metal layer;and metal in said recess such that said metal provides an electricalcontact to said top metal layer; wherein said recess is T-shaped, withthe vertical portion of said T being said contacting portion.
 6. Avertical capacitor contact arrangement for making electrical contact toa vertical capacitor on a first integrated circuit (IC), said verticalcapacitor having a top metal and a bottom metal separated by adielectric, and at least one trench, comprising: a first oxide layerover said vertical capacitor; a recess in said first oxide layer whichprovides access to said vertical capacitor's top metal layer, saidrecess having a contacting portion which contacts said top metal layer;and metal in said recess such that said metal provides an electricalcontact to said top metal layer; wherein said recess is T-shaped, withthe horizontal top portion of said T-shaped recess having a top surfacearea that is sufficient for subsequent bonding processes.
 7. The contactarrangement of claim 1, wherein said recess provides access to saidvertical capacitor's bottom metal.
 8. A vertical capacitor contactarrangement for making electrical contact to a vertical capacitor on afirst integrated circuit (IC), said vertical capacitor having a topmetal and a bottom metal separated by a dielectric, and at least onetrench, comprising: a first oxide layer over said vertical capacitor; arecess in said first oxide layer which provides access to one of saidvertical capacitor's top or bottom metal layers; and metal in saidrecess such that said metal provides an electrical contact to the top orbottom metal layer to which said recess provides access; wherein saidtop and bottom metal layers are TiN.
 9. A vertical capacitor contactarrangement for making electrical contact to a vertical capacitor on afirst integrated circuit (IC), said vertical capacitor having a topmetal and a bottom metal separated by a dielectric, and at least onetrench, comprising: a first oxide layer over said vertical capacitor; arecess in said first oxide layer which provides access to one of saidvertical capacitor's top or bottom metal layers; and metal in saidrecess such that said metal provides an electrical contact to the top orbottom metal layer to which said recess provides access; furthercomprising a second IC having an electrical contact arranged to contactsaid electrical contact to the top or bottom metal layer to which saidrecess provides access when said first and second ICs are aligned in apredetermined manner.
 10. The contact arrangement of claim 9, whereinsaid electrical contacts on said first and second ICs are copper andsaid copper electrical contacts on said first and second ICs bond saidfirst and second ICs together.
 11. The contact arrangement of claim 9,wherein said first IC comprises a vertical capacitor array and saidsecond IC is a readout IC (ROIC).
 12. The contact arrangement of claim11, further comprising a third IC comprising an array of photodetectors,said vertical capacitor array arranged to store charge produced by saidarray of photodetectors.
 13. A vertical capacitor contact arrangementfor making electrical contact to a vertical capacitor on a firstintegrated circuit (IC), said vertical capacitor having a top metal anda bottom metal separated by a dielectric, and at least one trench,comprising: a first oxide layer over said vertical capacitor; a recessin said first oxide layer which provides access to one of said verticalcapacitor's top or bottom metal layers; and metal in said recess suchthat said metal provides an electrical contact to the top or bottommetal layer to which said recess provides access; wherein said first ICincludes a substrate, said vertical capacitor being on said substrate,further comprising dummy capacitors tiled on portions of said first ICwhere there are no vertical capacitors, said dummy capacitors arrangedsuch that the top surfaces of their top metal are at a heightapproximately equal to that of the top surface of said verticalcapacitor's top metal.
 14. A vertical capacitor contact arrangement formaking electrical contact to a vertical capacitor on a first integratedcircuit (IC), said vertical capacitor having a top metal and a bottommetal separated by a dielectric, and at least one trench, comprising: afirst oxide layer over said vertical capacitor; a recess in said firstoxide layer which provides access to one of said vertical capacitor'stop or bottom metal layers; and metal in said recess such that saidmetal provides an electrical contact to the top or bottom metal layer towhich said recess provides access; further comprising a planarized oxidelayer over said first oxide layer.
 15. A vertical capacitor contactarrangement for making electrical contact to a vertical capacitor on afirst integrated circuit (IC), said vertical capacitor having a topmetal and a bottom metal separated by a dielectric, and at least onetrench, comprising: a first oxide layer over said vertical capacitor; arecess in said first oxide layer which provides access to one of saidvertical capacitor's top or bottom metal layers; and metal in saidrecess such that said metal provides an electrical contact to the top orbottom metal layer to which said recess provides access; wherein thedielectric layer between said vertical capacitor's top and bottom metalscomprises hafnium oxide and said first oxide layer comprises silicondioxide.
 16. A vertical capacitor array, comprising: an integratedcircuit (IC) having a substrate on which an array of vertical capacitorshas been fabricated, each of said vertical capacitors having a top metaland a bottom metal separated by a dielectric, and at least one trench; afirst oxide layer over said array of vertical capacitors; a plurality ofrecesses in said first oxide layer, each of which provides access to thetop or bottom metal layer of a respective one of said verticalcapacitors; and copper in said recesses such that, for each of saidrecesses, said copper provides electrical contacts to said verticalcapacitors' the top or bottom metal layers to which said recess providesaccess.
 17. The vertical capacitor array of claim 16, wherein each ofsaid vertical capacitors comprise at least two adjacent trenches, saidrecesses which provide access to said vertical capacitors' top metalbeing T-shaped with the vertical portions of said Ts contacting saidcapacitors' top metal and being approximately centered between adjacenttrenches such that there is no overlap between said vertical portionsand any of said trenches.
 18. The vertical capacitor array of claim 16,further comprising a second IC having one or more copper electricalcontacts arranged to contact respective ones of said copper electricalcontacts on said first IC when said first and second ICs are aligned ina predetermined manner, said copper electrical contacts on said firstand second ICs bonding said first and second ICs together.
 19. Thevertical capacitor array of claim 18, wherein said second IC is areadout IC (ROIC).
 20. The vertical capacitor array of claim 19, furthercomprising a third IC comprising an array of photodetectors, saidvertical capacitor array arranged to store charge produced by said arrayof photodetectors.
 21. A method of fabricating a vertical capacitorarray, comprising: providing a substrate; patterning and etchingtrenches in said substrate; depositing a bottom metal layer in saidtrenches; depositing a dielectric layer over said bottom metal layer;depositing a top metal layer over said dielectric layer; depositing afirst oxide layer over said top metal layer; etching recesses in saidfirst oxide layer to provide access to said top and bottom metal layers,each of said recesses providing access to a top metal layer having acontacting portion which contacts said top metal; depositing copper onsaid first oxide layer and in said recesses; and patterning and etchingsaid copper to remove copper that is not in said recesses, said copperin said recesses providing electrical contacts to said top and bottommetal layers.
 22. The method of claim 21, wherein each of said recessesis T-shaped with the vertical portions of said Ts being said contactingportions, said contacting portions approximately centered betweenadjacent ones of said trenches such that there is no overlap betweensaid contacting portions and any of said trenches.
 23. The method ofclaim 21, wherein each of said recesses is T-shaped, with the horizontaltop portion of each T-shaped recess having a top surface area that issufficient for subsequent bonding processes.
 24. The method of claim 21,further comprising depositing a second oxide layer over said first oxidelayer, said recesses etched through said first and second oxide layers.25. The method of claim 24, further comprising planarizing said firstand second oxide layers prior to etching said recesses.
 26. The methodof claim 21, further comprising depositing a seed layer in said recessesprior to depositing copper in said recesses.
 27. The method of claim 26,wherein said seed layer comprises tantalum and copper.
 28. The method ofclaim 21, further comprising fabricating dummy capacitors on portions ofsaid substrate where there are no vertical capacitors, said dummycapacitors arranged such that the top surfaces of their top metal are ata height approximately equal to that of the top surface of said verticalcapacitors' top metal.
 29. A method of fabricating a vertical capacitorarray, comprising: providing a substrate; patterning and etchingtrenches in said substrate; depositing a bottom metal layer in saidtrenches; depositing a dielectric layer over said bottom metal layer;depositing a top metal layer over said dielectric layer, thereby formingat least one vertical capacitor; fabricating dummy capacitors onportions of said substrate where there are no vertical capacitors, saiddummy capacitors arranged such that the top surfaces of their top metalare at a height approximately equal to that of the top surface of saidvertical capacitors' top metal; depositing a first oxide layer over saidtop metal layer; depositing a second oxide layer over said first oxidelayer; planarizing said first and second oxide layers; etching recessesin said first and second oxide layers to provide access to said top andbottom metal layers, each of said recesses providing access to a topmetal layer being T-shaped, with the vertical portion of said Tcontacting said top metal and approximately centered between adjacentones of said trenches; depositing copper on said first and second oxidelayers and in said recesses; patterning and etching said copper toremove copper that is not in said recesses, said copper in said recessesproviding electrical contacts to said top and bottom metal layers. 30.The method of claim 29, wherein said recesses are etched such that thereis no overlap between said vertical portions and any of said trenches.